Multiprotocol Label Switching (MPLS) is an Internet Task Force (IETF)-specified mechanism that provides for the designation, routing, forwarding and switching of traffic flows through a network. In a MPLS network, each data packets is assigned a label, and each data packet is directed from one network node to the next based on a short path label, rather than a long network address. Under the MPLS framework, data transmission occurs on Label-Switched Paths (LSPs), and LSPs are a sequence of labels at each and every node along a path from a source to the destination. The labels identify virtual links (paths) between distant nodes rather than endpoints. MPLS can encapsulate packets of various network protocols. MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay and DSL.
Label Distribution Protocol (LDP) is a protocol defined by RFC 5036 of the IETF for the purpose of distributing labels in an MPLS environment. Routers in the MPLS are referred to as label switching routers (LSR) and use LDP to establish LSPs. Routers having an established session are called LDP peers and the exchange of information is bi-directional. LDP is used to build and maintain LSP databases that are used to forward traffic through MPLS networks.